Epoxy paste composition including a silver-coated copper nanowire having core-shell structure, and conductive film including same

ABSTRACT

The present invention relates to an epoxy paste composition including silver-coated copper nanowires having a core-shell structure, and a conductive film including the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase of International PatentApplication Serial No. PCT/KR2017/012115 entitled “EPOXY PASTECOMPOSITION INCLUDING SILVER-COATED COPPER NANOWIRES HAVING CORE-SHELLSTRUCTURE, AND CONDUCTIVE FILM INCLUDING SAME,” filed on Oct. 31, 2017.International Patent Application Serial No. PCT/KR2017/012115 claimspriority to Korean Patent Application No. 10-2016-0144890, filed on Nov.2, 2016. The entire contents of each of the above-cited applications arehereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present invention relates to an epoxy paste composition using asilver-coated copper nanowire having a core-shell structure, and aconductive film including the same. In detail, the present inventionrelates to an epoxy paste composition including a silver-coated coppernanowire having a core-shell structure, an epoxy resin, and a curingagent, which is a conductive paste composition having economicefficiency, an excellent electrical characteristic, and a short curingtime, and a conductive film formed thereof.

BACKGROUND ART

A silver paste refers to a conductive paste in which a silver power iscontained as a filler. Here, the conductive paste refers to a conductiveprinting ink, a coating material such as paint, and a product line suchas an adhesive. DuPont was the first in the world develop these productsand had the biggest market share in the world until 20 to 30 years ago.However, since, in 1955, Japanese Research Institute for ElectricalCommunication began to develop a conductive adhesive and paint and sellthe products to chemical companies in Japan, the number of manufacturershas increased. A method in which a conductive paste is applied orprinted on a film, a substrate, or a substrate of an electroniccomponent, and dry-cured by heating to form an electrode or electricwiring has been conventionally widely used. However, in accordance withthe recent trend toward a high performance of electronic devices, anelectrode, a wiring pattern, and the like formed using a conductivepaste are demanded to have a lower resistance, and the demand has beenstrengthened every year.

As an epoxy paste, a 2-component epoxy resin-based conductive pasteincluding an epoxy resin, in which a conductive metal powder isdispersed, and a curing agent has been conventionally widely used.However, since the epoxy resin and the curing agent should be mixedimmediately before use of the 2-component epoxy resin-based conductivepaste, the 2-component epoxy resin-based conductive paste is difficultto use.

In addition, for exhibiting conductivity required for the conductivepaste, a sufficient amount of conductive powder needs to be dispersed inthe epoxy resin when preparing. However, the use of a large amount ofconductive powder was not preferable due to high cost and weak physicalproperties such as brittleness. Conventionally, silver nanoparticles orsilver flakes having a size of several nanometers to several tens ofmicrometers have been used as the conductive powder. However, such amaterial of the silver powder has a low electrical resistance but isexpensive. Therefore, development of the material is required to replacesilver when preparing a conductive paste.

Accordingly, the present inventors have made efforts to solve the aboveproblems, and as a result, have found that in a case where an epoxypaste composition is prepared using a silver-coated copper nanowirehaving a core-shell structure as a filler, it is possible to prepare anepoxy paste composition which has an excellent adhesiveness to asubstrate, may have a high conductivity even when dried at a lowtemperature, has a short curing time, and has an excellent economicefficiency and productivity, and completed the present invention.

DISCLOSURE Technical Problem

In order to solve the above problems, an object of the present inventionis to provide an epoxy paste composition including a silver-coatedcopper having a core-shell structure which has an excellent economicefficiency and conductivity, and a short curing time.

In addition, another object of the present invention is to provide aconductive film having a low specific resistance and a highelectromagnetic interference shielding effectiveness produced byapplying an epoxy paste composition including a silver-coated coppernanowire having a core-shell structure on a substrate, and thenperforming a heat treatment.

Technical Solution

As a result of research for achieving the above objects, the presentinventors found an epoxy paste composition including a silver-coatedcopper nanowire having a core-shell structure, an epoxy resin, and acuring agent, and a conductive film formed thereof, which cansignificantly lower a specific resistance and improve an electromagneticinterference shielding effectiveness, and completed the presentinvention.

In one general aspect, an epoxy paste composition includes: 55 to 70 wt% of a silver-coated copper nanowire having a core-shell structure; 1 to35 wt % of an epoxy resin; and 1 to 35 wt % of a curing agent.

An amount of silver is 2 to 60 parts by weight based on 100 parts byweight of a total amount of the silver-coated copper nanowire.

A ratio (f/a) of the largest diameter (f) of a cross section of thesilver-coated copper nanowire perpendicular to a length direction to alength (a) of the silver-coated copper nanowire may be 0.0001 to 0.06.

The curing agent may be any one or two or more selected from the groupconsisting of an acid anhydride-based curing agent, a phenol-basedcuring agent, an imidazole-based curing agent, and an amino-based curingagent.

The epoxy resin may be any one or two or more selected from the groupconsisting of a bisphenol A type epoxy resin, a bisphenol F type epoxyresin, a bisphenol S type epoxy resin, a phenol novolac type epoxyresin, a cresol novolac type epoxy resin, an alkylphenol novolac typeepoxy resin, a biphenyl type epoxy resin, a naphthalene type epoxyresin, a dicyclopentadiene type epoxy resin, triglycidyl isocyanate, anurethane-modified epoxy resin, and a non-aromatic epoxy resin.

The epoxy paste composition may further include a diluent, and thediluent may be any one or two or more selected from the group consistingof acetone, methyl ethyl ketone, methyl alcohol, ethyl alcohol,isopropyl alcohol, butyl alcohol, ethylene glycol, polyethylene glycol,tetrahydrofuran, dimethylformamide, dimethylacetamide,N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform,dichlorobenzene, dimethylbenzene, trimethylbenzene, pyridine,methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, aniline,dimethyl sulfoxide, diethylene glycol ethyl ether, and terpineol.

In another general aspect, a conductive film may be produced by applyingthe epoxy paste composition on a substrate and performing a heattreatment.

The heat treatment may be performed at 100 to 200° C. for 20 to 60minutes.

A specific resistance of the conductive film may be 1.0×10⁻⁵ to 6.0×10⁻⁶Ω·m, and an electromagnetic interference shielding effectiveness of theconductive film at 1500 MHz may be 20 to 70 dB.

Advantageous Effects

The epoxy paste composition according to the present invention includesa silver-coated copper nanowire, such that the epoxy paste compositionhas oxidation stability and thermal stability. Therefore, the epoxypaste composition has a binding force with the epoxy resin and a highdispersibility. Accordingly, the epoxy paste composition has anexcellent electrical conductivity and a short curing time due to a lowsheet resistance and specific resistance, which may realize an excellentconductivity and electromagnetic interference shielding property. Inaddition, with the advantages described above, the epoxy pastecomposition may be widely used in various fields such as anelectromagnetic interference shielding and an absorbing product, anelectrode, an electronic circuit, an antenna, and the like.

DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph obtained by observing a substrate coated with anepoxy paste composition including a silver-coated copper nanowireaccording to an example of the present invention with a scanningelectron microscope (SEM).

FIG. 2 is a photograph obtained by observing a substrate coated with anepoxy paste composition including silver flakes according to acomparative example of the present invention with a scanning electronmicroscope (SEM).

FIG. 3 is graph showing data of measurements of an electromagneticinterference shielding effectiveness of a conductive film produced bycoating a substrate with an epoxy paste composition according to anexample of the present invention.

BEST MODE

Hereinafter, an epoxy paste composition including a silver-coated coppernanowire having a core-shell structure according to an embodiment of thepresent invention, and a conductive film including the same will bedescribed in more detail. However, the following embodiments are only areference example for describing the present invention in detail, andthe present invention is not limited thereto and may be implemented invarious forms.

In addition, unless otherwise defined, all terms of technical andscientific terms used herein have the same meaning as commonlyunderstood by one of those skilled in the art to which the presentinvention pertains. The terms used herein are only for effectivelydescribing a certain embodiment rather than limiting the presentinvention.

The term “nanowire” in the present specification refers to a filler inwhich a silver-coated copper nanowire used as a conductive filler has adiameter measured in nanometers and a long shape similar to a wire.

The term “silver-coated copper nanowire” in the present specificationrefers to a nanowire having a core-shell structure including a coreformed of a copper nanowire and a shell formed of silver.

The present invention in order to achieve the above object relates to anepoxy paste composition including a silver-coated copper nanowire havinga core-shell structure, and a conductive film including the same.

The present invention will be described in detail.

The epoxy paste composition in the present invention may include 55 to70 wt % of a silver-coated copper nanowire having a core-shellstructure, 1 to 35 wt % of an epoxy resin, and 1 to 35 wt % of a curingagent. The epoxy paste composition in the present invention maypreferably include 60 to 70 wt % of a silver-coated copper nanowirehaving a core-shell structure, 10 to 35 wt % of an epoxy resin, and 10to 35 wt % of a curing agent.

Since the epoxy paste composition described above includes thesilver-coated copper nanowire, the epoxy resin, and the curing agent,although the exact reason is not known, surprisingly, the epoxy pastecomposition in the present invention has an excellent oxidationstability and thermal stability, such that a binding force with theepoxy resin and a high dispersibility may be improved. Accordingly, theepoxy paste composition has a high electrical conductivity due to thesignificantly lowered specific resistance and the sheet resistance, andconductivity is significantly improved when the substrate is applied,such that the conductive film may have an excellent conductivity andelectromagnetic interference shielding property.

When a content of the silver-coated copper nanowire included in theepoxy paste composition is in the range of 55 to 70 wt %, and preferably60 to 70 wt % based on a total content of the epoxy paste composition,the epoxy paste composition may have a high conductivity when beingcoated on the substrate, and a non-uniform dispersion of thesilver-coated copper nanowire due to a high viscosity of the compositionmay be prevented, which is preferable.

The nanowire having a core-shell structure according to the presentinvention is a silver-coated copper nanowire having a core-shellstructure including a core formed of a copper nanowire and a shellformed of silver, and has an excellent oxidation stability and thermalstability in comparison to a conventional copper nanowire, for example,a copper nanowire not coated with silver, a spherical particle, a flakeshape, or the like.

In addition, the nanowire having a core-shell structure has a gooddispersibility due to the shape thereof in comparison to a metalnanoparticle. Since the shape of the nanowire is different from that ofthe particle or the flakes, a sheet resistance of a conductive film maybe significantly lowered. Further, a production cost may be reduced byusing a silver-coated copper nanowire in comparison to using a silvernanowire.

According to an aspect of the present invention, an amount of silver maybe 2 to 60 parts by weight based on 100 parts by weight of a totalamount of the silver-coated copper nanowire. When silver is coated inthe content described above, the copper nanowire may be uniformly coatedwith the silver, has an excellent oxidation stability and thermalstability, and may prevent generation of a separate silver particlegenerated by including excess silver, which is preferable.

According to an aspect of the present invention, a ratio (f/a) of thelargest diameter (f) of a cross section of the silver-coated coppernanowire perpendicular to a length direction on to a length (a) of thesilver-coated copper nanowire may be 0.0001 to 0.06, but is not limitedthereto.

When the ratio (f/a) is within the range described above, a highconductivity of the epoxy paste composition may be realized even at alow density of the nanowire, and a sheet resistance and specificresistance may be lowered after curing, which is preferable.

In detail, a length of the silver-coated copper nanowire may be 5 to 10μm and a diameter of the silver-coated copper nanowire may be 200 to 300nm, but is not limited thereto.

When the silver-coated copper nanowire has the diameter of the rangedescribed above, a high ratio (f/a) is secured, such that a conductivefilm having a high conductivity and a low sheet resistance may beimplemented. Further, an electron movement path having a large arearelative to a surface area of the silver-coated copper nanowires issecured, such that electrical characteristics may be improved and thesilver-coated copper nanowire has flexibility, which is preferable.

When the silver-coated copper nanowire has the length of the rangedescribed above, a high ratio (f/a) is secured, such that a conductivefilm having a high conductivity and a low sheet resistance may beimplemented. Further, a connection length at which the silver-coatedcopper nanowires are in contact with each other is secured, such thatelectrical characteristics may be improved and physical breakage of thesilver-coated copper nanowire may be prevented when coating thesubstrate, which is preferable.

In a case where the epoxy paste composition includes 1 to 35 wt % of anepoxy resin, and preferably 10 to 30 wt % of an epoxy resin based on thetotal content of the epoxy paste composition, the epoxy pastecomposition according to the present invention may be prevented frombeing peeled off from the substrate due to a high adhesion to asubstrate when being coated on the substrate and may preventdeterioration in conductivity due to an excess epoxy resin without lossof inherent physical properties of the epoxy resin, which is preferable.

According to an aspect of the present invention, the epoxy resin may beany one or two or more epoxy resins selected from the group consistingof a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, abisphenol S type epoxy resin, a phenol novolac type epoxy resin, acresol novolac type epoxy resin, an alkylphenol novolac type epoxyresin, a biphenyl type epoxy resin, a naphthalene type epoxy resin, adicyclopentadiene type epoxy resin, triglycidyl isocyanate, anurethane-modified epoxy resin, and an epoxy resin, but is not limitedthereto.

In addition, in a case where the epoxy paste composition includes 1 to35 wt % of a curing agent, and preferably 10 to 30 wt % of a curingagent based on the total content of the epoxy paste composition, theepoxy paste composition according to the present invention may have ashort curing time and does not require a high curing temperature, whichis preferable. Further, since curing caused by a small impact orstimulation does not occur, it is easy to store the epoxy pastecomposition, which is preferable.

According to an aspect of the present invention, the curing agent may beany one or two or more selected from the group consisting of an acidanhydride-based curing agent, a phenol-based curing agent, animidazole-based curing agent, and an amino-based curing agent, but isnot limited thereto.

In a specific example of the curing agent, as the acid anhydride-basedcuring agent, any one or two or more selected from the group consistingof phthalic anhydride, maleic anhydride, trimellitic anhydride,pyromellitic anhydride, hexahydrophthalic anhydride, tetrahydrophthalicanhydride, methyl nadic anhydride, nadic anhydride, glutaric anhydride,methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride,and the like may be used.

As the phenol-based curing agent, any one or two or more selected fromthe group consisting of phenol resins such as a formaldehyde condensedresol type phenol resin, a non-formaldehyde condensed phenol resin, anovolac-type phenol resin, a novolac-type phenol formaldehyde resin, anda polyhydroxystyrene resin; resol type phenol resins such as ananiline-modified resol resin and a melamine-modified resol resin;novolac-type phenol resins such as a phenol novolac resin, a cresolnovolac resin, a tert-butylphenol novolac resin, a nonylphenol novolacresin, and a naphthol novolac resin; special phenol resins such as adicyclopentadiene-modified phenol resin, a terpene-modified phenolresin, a triphenolmethane-type resin, and a phenol aralkyl resin and anaphthol aralkyl resin having a phenylene skeleton or a diphenyleneskeleton; polyhydroxystyrene resins such as a poly(p-hydroxystyrene)resin; and the like may be used.

The amino-based curing agent may be any one or two or more selected fromthe group consisting of dimethyl dicykan (DMDC), dicyandiamide (DICY),isophorone diamine (IPDA), diethylenetriamine (DETA),triethylenetetramine (TETA), bis(p-aminocyclohexyl) methane (PACM),methylenedianiline (for example, 4,4′-methylenedianiline),polyetheramine, for example, polyetheramine D230, diaminodiphenylmethane(DDM), diaminodiphenylsulfone (DDS), 2,4-toluenediamine,2,6-toluenediamine, 2,4-diamino-1-methylcyclohexane,2,6-diamino-1-methylcyclohexane, 2,4-diamino-3,5-diethyltoluene,2,6-diamino-3,5-diethyltoluene, 1,2-diaminobenzene, 1,3-diaminobenzene,1,4-diaminobenzene, diamino diphenyl oxide,3,3′,5,5′-tetramethyl-4,4′-diaminobiphenyl,3,3′-dimethyl-4,4′-diaminodiphenyl, and the like. As the amino-basedcuring agent, any one or two or more selected from the group consistingof dimethyl dicykan (DMDC), dicyandiamide (DICY), isophorone diamine(IPDA), and methylenedianiline may be used.

According to an aspect of the present invention, the epoxy pastecomposition may further include a diluent. A content of the diluent maybe adjusted depending on a viscosity of the epoxy paste, and a contentof diluent may be preferably 15 to 30 parts by weight with respect tototal 100 parts by weight of the epoxy paste composition, but is notlimited thereto. In a case where the content of the diluent is in therange described above, since the epoxy paste composition has a viscositywhich can be uniformly applied when coating is performed, thesilver-coated copper nanowire may be uniformly dispersed, such that theconductive film has a high electrical conductivity and an improvedelectromagnetic interference shielding property, which is preferable.The diluent may be any one or two or more selected from the groupconsisting of acetone, methyl ethyl ketone, methyl alcohol, ethylalcohol, isopropyl alcohol, butyl alcohol, ethylene glycol, polyethyleneglycol, tetrahydrofuran, dimethylformamide, dimethylacetamide,N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform,dichlorobenzene, dimethylbenzene, trimethylbenzene, pyridine,methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, butylcarbitol acetate, aniline, dimethyl sulfoxide, diethylene glycol ethylether, and terpineol.

The epoxy paste composition in the present invention may be uniformlyapplied when applied on a substrate, such as coating, casting, and thelike, and may be prepared to have a viscosity of 300,000 to 400,000 cpsmeasured at 25° C. so as to improve processability.

The conductive film in the present invention may be a conductive film inwhich a substrate is applied with the epoxy paste composition andsubjected to a heat treatment.

Specifically, the substrate is applied with the epoxy paste compositionincluding 55 to 70 wt % of a silver-coated copper nanowire having acore-shell structure, 1 to 35 wt % of an epoxy resin, and 1 to 35 wt %of a curing agent and may be subjected to a heat treatment. Preferably,the substrate is applied with the epoxy paste composition including 60to 70 wt % of a silver-coated copper nanowire having a core-shellstructure, 10 to 30 wt % of an epoxy resin, and 10 to 30 wt % of acuring agent and may be subjected to the heat treatment.

The substrate may be a substrate formed of an organic or inorganicmaterial, and specifically, may be a plastic substrate, a glasssubstrate, or a quartz substrate. Examples of materials constituting thesubstrate may be selected from a methacrylic resin, aromatic polyester,modified polyphenylene oxide (MPPO), cellulose ester, cellulose acetate,quartz, a styrene-butadiene copolymer, silicon wafer, acrylonitrilebutadiene styrenecopolymer (ABS resin), an epoxy resin, an olefinmaleimide copolymer, fused silica, glass, regenerated cellulose,triacetyl cellulose, a phenol resin, polydimethyl cyclohexeneterephthalate, polydimethylsiloxane (PDMS), polymethylmethacrylate,polymethylacrylate, polybutadiene, polybutylene terephthalate,polyvinylidene fluoride, polyvinyl acetate, polysulfonate, polysulfone,polystyrene (PS), polysilazane, polysilane, polysiloxane, polyaramid,polyarylate, polyamide, polyamide-imide, polyacrylate, polyacrylonitrile(PAN), polyester, polyethersulfone (PES), polyether nitrile, polyethersulfone, polyether imide, polyether ketone, polyethylenenaphthalte(PEN), polyethylene sulfone, polyethylene (PE), polyethyleneterephtalate (PET), polyethylmetacrylate, polyethylacrylate,polyepoxide, polyvinyl chloride, polyoxyethylene, polyolefin,polyurethane, a polyimide resin, polycarbosilane, polycarbonate,polyphenylene sulfide, polyphenylene ether, polypropylene (PP), an ASresin, GaAs, MaO, silica, polycarbon, and the like, but are not limitedthereto.

The substrate according to an aspect may be selectively subjected to anadditional surface treatment by using at least one method of a Piranhasolution treatment method, an acid treatment method, a base treatmentmethod, an atmospheric plasma treatment method, an ozone treatmentmethod, an ultraviolet (UV) treatment method, a self assembled monolayer(SAM) treatment method, and a polymer or monomolecular coating method.

The heat treatment in the present invention may be performed at 100 to200° C. for 10 to 60 minutes. A curing reaction of the epoxy pastecomposition occurs during the heat treatment process. At this time, thecuring reaction may include a semi-curing reaction of a reactionmaterial. As described above, in the case where the semi-curing reactionproceeds when the heat treatment is performed, an additional curingreaction further proceeds as a process subsequent to a pressurizingprocess such as laminating and hot pressing, such that a complete curedreaction product may be obtained.

The heat treatment is preferably performed at 100 to 200° C., morepreferably 120 to 200° C., still more preferably 150 to 200° C. forphysical properties of the film.

In addition, the epoxy paste composition in the present invention may beheat-treated preferably within 10 to 60 minutes, more preferably 10 to40 minutes, and still more preferably 10 to 30 minutes. Even though theepoxy paste composition is cured in a short time, a low specificresistance and sheet resistance are constant without increasing;therefore, the epoxy paste composition may have an excellent economicefficiency and productivity.

The epoxy paste composition in the present invention may be coated tothe substrate through an application method selected from a spraycoating method, a gravure coating method, a microgravure coating method,a bar-coating method, a knife coating method, a reverse roll coatingmethod, a roll coating method, a calender coating method, a curtaincoating method, an extrusion coating method, a cast coating method, adip coating method, an air-knife coating method, a foam coating method,a slit coating method, and the like, but is not limited thereto.

According to an aspect of the present invention, in order forimprovements in electromagnetic interference shielding ability, bendingproperty, an adhesive force, and interlayer adhesion and uniformapplication to the substrate, the epoxy paste composition may be appliedon the substrate at a thickness of 50 to 200 μm, and preferably 50 to150 μm.

According to an aspect of the present invention, in order forimprovements in electromagnetic interference shielding ability, bendingproperty, an adhesive force, and interlayer adhesion of the conductivefilm, the thickness of the conductive film may be 1 to 100 μm, andpreferably 25 to 80 μm.

When the conductive film produced using the epoxy paste composition inthe present invention has a thickness of 1 to 100 μm, a specificresistance of the conductive film may be 1.0×10⁻⁵ to 6.0×10⁻⁶ Ω·m, andan electromagnetic interference shielding effectiveness of theconductive film at 1500 MHz may be 20 to 70 dB. Preferably, in order tohave an excellent electrical conductivity and electromagneticinterference shielding ability in the conductive film, when theconductive film produced using the epoxy paste composition in thepresent invention has a thickness of 25 to 80 μm, a specific resistanceof the conductive film may be 1.0×10⁻⁶ to 6.0×10⁻⁶ Ω·m, and anelectromagnetic interference shielding effectiveness of the conductivefilm at 1500 MHz may be 50 to 70 dB.

In the epoxy paste composition including the silver-coated coppernanowire having a core-shell structure according to the presentinvention having the configuration described above, the silver-coatedcopper nanowire having a core-shell structure has an excellent bindingforce with the epoxy resin and dispersibility, although the exact reasonis not known, surprisingly, the conductive film has a high electricalconductivity due to the significantly lowered specific resistance andthe sheet resistance, and conductivity is significantly improved whenthe substrate is applied, such that the conductive film may have anexcellent conductivity and electromagnetic interference shieldingproperty.

Hereinafter, an epoxy paste composition including a silver-coated coppernanowire having a core-shell structure according to examples of thepresent invention, and the epoxy paste composition including the samewill be described in more detail. However, the following examples andcomparative examples are only one reference example for describing thepresent invention in detail, the present invention is not limitedthereto, and may be implemented in various forms.

Unless otherwise defined, all terms of technical and scientific termsused herein have the same meaning as commonly understood by one of thoseskilled in the art to which the present invention belongs. The termsused herein are only for effectively describing a certain example ratherthan limiting the present invention.

Further, unless otherwise stated in the specification, the unit of addedmaterials may be wt %.

[Physical Property Measurement Method]

1) Form and structure measurement: A coating form of an epoxy pastecomposition using a silver-coated copper nanowire having a core-shellstructure was measured with a scanning electron microscope (SEM) (FEI,SIRION).

2) Sheet resistance: In order to compare electrical conductivities, asheet resistance of the conductive film produced by the followingexamples was measured with a four-point probe sheet resistance meter(Loresta-GP, MCP-T610, MITSUBISHI CHEMICAL ANALYTECH). When measuringthe sheet resistance of the conductive film with the four-point probesheet resistance meter, the measurement was performed by dividing thefilm into four parts, and then an average value was obtained. A specificresistance was calculated by applying a film thickness to the measuredsheet resistance value.

3) Paste coating: A polyimide film was coated with the prepared epoxypaste composition using a bar coater (ERICHSEN, Model-510).

4) Film thickness measurement: The film thickness was measured with athickness gauge (ERICHSEN, Foil Thickness Gauge Model 497).

5) electromagnetic interference shielding effectiveness measurement: Inorder to measure an electromagnetic interference shielding effectivenessof the conductive film, the electromagnetic interference shieldingeffectiveness was measured using a network analyzer (Protek, A333).

Example 1

8 g of a silver-coated copper nanowire having a core-shell structure(BIONEER CORPORATION), 2 g of an epoxy resin (SE-55F, SHIN-A T&C), 3 gof a curing agent (XHT-1004, SHIN-A T&C), 2.5 g of terpineol(α-terpineol, SAMCHUN CHEMICALS), and 0.5 g of butyl carbitol acetate(SAMCHUN CHEMICALS) were put into a 100 ml Erlenmeyer flask and stirredwith a revolution-rotation mixer (ARE-310, THINKY) at 2000 rpm for 30minutes. Then, an epoxy paste composition was prepared by performingdispersion treatments five times using a 3-rollmill (EXAKT 50).

In order to perform a conductive test for the epoxy paste compositionprepared in Example 1, 10 ml of the epoxy paste composition was appliedon a polyimide film of 100 mm×100 mm, and then coating was performedusing a bar coater capable of coating a film at a wet thickness of 100μm. The produced conductive film was heated in a dry oven at atemperature rising rate of 2° C./min up to 150° C., and then, in orderto examine a dry condition, the conductive films were prepared by beingsubjected to a heat treatment at 150° C. for 15 minutes, 30 minutes, and60 minutes. At this time, the final thickness of the dried epoxy pastecomposition was 20 μm.

When the entire epoxy paste composition was prepared as in the conditionof Example 1, as shown in Table 1, the specific resistance of 4.6×10⁻⁶Ω·m was constantly measured even when the curing time was increased from15 minutes to 60 minutes. Therefore, it was confirmed that curing may beperformed in a short time under the optimal condition of a temperatureof 150° C. and a curing time of 15 minutes, such that economicefficiency and productivity may be improved.

Example 2

Example 2 was performed in the same manner as in Example 1, except that11 g of a silver-coated copper nanowire was used.

It was confirmed that, 4.9×10⁻⁶ Ω·m of a specific resistance of an epoxypaste composition prepared in Example 2 was measured without change overa heat treatment time as shown in Table 1.

Example 3

Example 3 was performed in the same manner as in Example 1, except that1.5 g of a curing agent was used.

It was confirmed that, in an epoxy paste composition prepared in Example3, a specific resistance of a conductive film was changed depending onthe curing condition when the epoxy paste composition is used inproduction of the conductive film. In the case where the heat treatmentwas performed at 150° C. for 15 minutes, the specific resistance of theconductive film was 1.2×10⁻⁵ Ω·m, in the case where the heat treatmentwas performed at 150° C. for 30 minutes, the specific resistance of theconductive film was lowered to 9.9×10⁻⁶ Ω·m, and in the case where theheat treatment was performed at 150° C. for 60 minutes, the specificresistance of the conductive film was further lowered slightly to9.0×10⁻⁶ Ω·m. Accordingly, it was confirmed that the curing time isrequired to be increased as the content of the curing agent isdecreased.

Example 4

Example 4 was performed in the same manner as in Example 1, except that3.5 g of a curing agent was used.

It was confirmed that in an epoxy paste composition prepared in Example4, a specific resistance of a conductive film was almost not changedeven though the curing time was increased when the epoxy pastecomposition is used in production of the conductive film. It can beconfirmed that the epoxy paste composition was cured within less than 15minutes due to an increase in the content of the curing agent in thepreparation of the epoxy paste composition. In addition, it wasconfirmed that physical properties of the epoxy paste composition in thepresent invention does not deteriorate even when the heat treatment isperformed additionally time after curing.

Comparative Example 1

Comparative Example 1 was performed in the same manner as in Example 1,except that silver flakes were used instead of the silver-coated coppernanowire.

The specific resistance in Example 1 was 4.6×10⁻⁶ Ω·m, whereas thespecific resistance in Comparative Example 1 was 2.4×10⁻⁴ Ω·m when theepoxy paste composition was prepared using silver flakes. It wasconfirmed that the specific resistance in Comparative Example 1 wasincreased two orders of magnitude as compared with Example 1. It wasconfirmed that a further low specific resistance may be obtained whenthe conductive film was produced using the epoxy paste compositionincluding the silver-coated copper nanowire. According to these results,it was confirmed that the epoxy paste composition prepared using thesilver-coated copper nanowire has a more excellent economic efficiencyand physical properties than those of the epoxy paste compositionprepared using silver flakes.

Comparative Example 2

Comparative Example 2 was performed in the same manner as in Example 1,except that a silver nanoparticle was used instead of the silver-coatedcopper nanowire.

The specific resistance in Example 1 was 4.6×10⁻⁶ Ω·m, whereas thespecific resistance in Comparative Example 2 was 4.2×10⁻⁴ Ω·m when theepoxy paste composition was prepared using silver nanoparticles, it wasconfirmed that the specific resistance in Comparative Example 2 wasincreased two orders of magnitude as compared with Example 1. It wasconfirmed that a further low specific resistance may be obtained whenthe conductive film was produced using the epoxy paste compositionincluding the silver-coated copper nanowire. According to these results,it was confirmed that the epoxy paste composition prepared using thesilver-coated copper nanowire has a more excellent economic efficiencyand physical properties than those of the epoxy paste compositionprepared using silver nanoparticles.

Comparative Example 3

Comparative Example 3 was performed in the same manner as in Example 1,except that a copper nanowire was used instead of the silver-coatedcopper nanowire.

The specific resistance in Example 1 was 4.6×10⁻⁶ Ω·m, whereas thespecific resistance in Comparative Example 3 was 6.7×10⁻² Ω·m when theepoxy paste composition was prepared using a copper nanowire, it wasconfirmed that the specific resistance in Comparative Example 3 wasincreased by four orders of magnitude as compared with Example 1. It wasconfirmed that a sheet resistance and specific resistance of theconductive film was sharply increased due to oxidation of the coppernanowire by the heat treatment when the epoxy paste composition wasproduced using the copper nanowire. According to these results, it wasconfirmed that, in a case where the conductive film was produced usingthe epoxy paste composition including a silver-coated copper nanowire, afurther low specific resistance of the conductive film may be obtainedin comparison to using of the copper nanowire.

Comparative Example 4

Comparative Example 4 was performed in the same manner as in Example 1,except that 5.5 g of a silver-coated copper nanowire was used.

It was confirmed that, in an epoxy paste composition prepared inComparative Example 4, since a content of the silver-coated coppernanowire was low, an area of an electron movement path was decreased,such that a specific resistance was increased.

Comparative Example 5

Comparative Example 5 was performed in the same manner as in Example 1,except that 15 g of a silver-coated copper nanowire was used.

Since viscosity of an epoxy paste composition prepared in ComparativeExample 5 was too high, components of the composition were not uniformlydispersed and the composition was not coated in a film shape, thereforea specific resistance value was not measured.

Comparative Example 6

Comparative Example 6 was performed in the same manner as in Example 1,except that 0.1 g of an epoxy resin was used.

In an epoxy paste composition prepared in Comparative Example 5, thefilm was peeled off due to deterioration in adhesiveness betweencomponents of the composition. Therefore a specific resistance value wasnot measured.

Comparative Example 7

Comparative Example 7 was performed in the same manner as in Example 1,except that 5 g of an epoxy resin was used.

It was confirmed that when a conductive film was produced using an epoxypaste composition prepared in Comparative Example 7 and a specificresistance was measured, the specific resistance was sharply increaseddue to decrease in contact between silver-coated copper nanowires by anincrease of a content of the epoxy resin.

TABLE 1 Dry condition 150° C., 150° C., 150° C., 15 min 30 min 60 minExample 1 (Ω · m) 4.4 × 10⁻⁶ 4.6 × 10⁻⁶ 4.6 × 10⁻⁶ Example 2 (Ω · m) 4.9× 10⁻⁶ 4.9 × 10⁻⁶ 4.9 × 10⁻⁶ Example 3 (Ω · m) 1.2 × 10⁻⁵ 9.9 × 10⁻⁶ 9.0× 10⁻⁶ Example 4 (Ω · m) 6.6 × 10⁻⁶ 6.4 × 10⁻⁶ 6.4 × 10⁻⁶ ComparativeExample 1 2.4 × 10⁻⁴ 2.4 × 10⁻⁴ 2.4 × 10⁻⁴ (Ω · m) Comparative Example 24.3 × 10⁻⁴ 4.2 × 10⁻⁴ 4.2 × 10⁻⁴ (Ω · m) Comparative Example 3 6.1 ×10⁻² 6.7 × 10⁻² 6.7 × 10⁻² (Ω · m) Comparative Example 4 3.9 × 10⁻⁴ 3.9× 10⁻⁴ 3.8 × 10⁻⁴ (Ω · m) Comparative Example 5 Non- Non- Non- (Ω · m)measurable measurable measurable Comparative Example 6 Non- Non- Non- (Ω· m) measurable measurable measurable Comparative Example 7 1.0 × 10⁻³1.1 × 10⁻³ 1.1 × 10⁻³ (Ω · m)

Experimental Example 1

Electromagnetic Interference Shielding Test Depending on Thickness

As the conductive films of Example 1, coated films having wetthicknesses of 100 μm and 200 μm were produced with a bar coater inorder to confirm electromagnetic interference shielding abilitydepending on a thickness of the conductive film.

After two conductive films having different thicknesses were prepared,an electromagnetic interference shielding test was conducted. As shownin FIG. 3, when the epoxy paste composition was coated at a thickness of30 μm, about 55 dB of the electromagnetic interference shieldingeffectiveness at 1500 MHz was measured. In addition, when the epoxypaste composition was coated at a thickness of 75 μm, about 70 dB of theelectromagnetic interference shielding effectiveness at 1500 MHz wasmeasured.

Accordingly, when the conductive film is produced using the epoxy pastecomposition in the present invention, an excellent conductivity andelectromagnetic interference shielding property may be realized. Inaddition, with the advantages described above, the epoxy pastecomposition may be widely applied to various fields such as anelectromagnetic interference shielding and an absorbing product, anelectrode, an electronic circuit, an antenna, and the like.

TABLE 2 Applica- Coating Shielding tion thick- Sheet Specific effective-thickness ness resistance resistance ness (μm) (μm) (Ω/□) (Ω · m) (dB)Example 1 100 30  1.6 × 10⁻¹ 4.8 × 10⁻⁶ 55 Example 1 200 75  6.4 × 10⁻²4.8 × 10⁻⁶ 70 Comparative 100 30 8.0 × 10⁰ 2.4 × 10⁻⁴ 20 Example 1Comparative 200 70 3.4 × 10⁰ 2.4 × 10⁻⁴ 30 Example 1 Comparative 100 281.5 × 10¹ 4.2 × 10⁻⁴ 15 Example 2 Comparative 200 68 6.2 × 10⁰ 4.2 ×10⁻⁴ 25 Example 2 Comparative 100 30 2.23 × 10²  6.7 × 10⁻² 5 Example 3Comparative 200 70 9.6 × 10¹ 6.7 × 10⁻² 10 Example 3

As shown in Tables 1 and 2, when the epoxy paste composition includes 55to 70 wt % of a silver-coated copper nanowire having a core-shellstructure, 1 to 35 wt % of an epoxy resin, and 1 to 35 wt % of a curingagent, it was confirmed that the conductive film has an excellentelectrical conductivity and a low sheet resistance and specificresistance, and has a high electromagnetic interference shieldingeffectiveness.

Hereinabove, in the present invention, although the epoxy pastecomposition including a silver-coated copper nanowire having acore-shell structure and the conductive film including the same havebeen described by specific matters and limited embodiments, they havebeen provided only for assisting in the entire understanding of thepresent invention. Therefore, the present invention is not limited tothe above embodiments, and various modifications and changes may be madeby those skilled in the art to which the present invention pertains fromthis description.

Therefore, the spirit of the present invention should not be limited tothese exemplary embodiments, but the claims and all of modificationequal or equivalent to the claims are intended to fall within the scopeand spirit of the present invention.

The invention claimed is:
 1. An epoxy paste composition comprising: 48to 58 wt % of a silver-coated copper nanowire having a core-shellstructure; 1 to 35 wt % of an epoxy resin; and 1 to 35 wt % of a curingagent; wherein within the weight % range, the silver-coated coppernanowire:the epoxy resin is included in a weight ratio of 4 to 5.5:1. 2.The epoxy paste composition of claim 1, wherein an amount of silver is 2to 60 parts by weight based on 100 parts by weight of a total amount ofthe silver-coated copper nanowire.
 3. The epoxy paste composition ofclaim 1, wherein a ratio (f/a) of a largest diameter (f) of a crosssection of the silver-coated copper nanowire perpendicular to a lengthdirection to a length (a) of the silver-coated copper nanowire is 0.0001to 0.06.
 4. The epoxy paste composition of claim 1, wherein the curingagent is any one or two or more selected from the group consisting of anacid anhydride-based curing agent, a phenol-based curing agent, animidazole-based curing agent, and an amino-based curing agent.
 5. Theepoxy paste composition of claim 1, wherein the epoxy resin is any oneor two or more selected from the group consisting of a bisphenol A typeepoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxyresin, a phenol novolac type epoxy resin, a cresol novolac type epoxyresin, an alkylphenol novolac type epoxy resin, a biphenyl type epoxyresin, a naphthalene type epoxy resin, a dicyclopentadiene type epoxyresin, triglycidyl isocyanate, an urethane-modified epoxy resin, and anon-aromatic epoxy resin.
 6. The epoxy paste composition of claim 1,further comprising a diluent, wherein the diluent is any one or two ormore selected from the group consisting of acetone, methyl ethyl ketone,methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol,ethylene glycol, polyethylene glycol, tetrahydrofuran,dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane,cyclohexanone, toluene, chloroform, dichlorobenzene, dimethylbenzene,trimethylbenzene, pyridine, methylnaphthalene, nitromethane,acrylonitrile, octadecylamine, butyl carbitol acetate, aniline, dimethylsulfoxide, diethylene glycol ethyl ether, and terpineol.
 7. A conductivefilm produced by applying the epoxy paste composition of claim 1 on asubstrate and curing.
 8. The conductive film of claim 7, wherein thecuring is performed at 100 to 200° C. for 20 to 60 minutes.
 9. Theconductive film of claim 7, wherein a specific resistance of theconductive film is 1.0×10⁻⁵ to 6.0×10⁻⁶ Ω·m, and an electromagneticinterference shielding effectiveness of the conductive film at 1500 MHzis 20 to 70 dB.
 10. An electromagnetic interference shielding filmproduced by applying the epoxy paste composition of claim 1 on asubstrate and curing.